Headup display

ABSTRACT

A headup display having an image forming unit  1  f or forming an item of image information to be displayed that can be projected as light beams  2  by the image forming unit  1  or via an optical projection system onto a partially reflecting windshield pane  7.  The image forming unit  1  has an OLED display  8  for forming the image information displayed, in front of which there is arranged a light directing element  14  by which the light beams  2  produced by the OLED display  8  can be directed approximately parallel to one another.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a headup display, in particular for a motorvehicle, having an image forming unit for forming an item of imageinformation to be displayed that can be projected as light beams by theimage forming unit directly or via an optical projection system onto apartially reflecting pane, in particular onto a windshield pane.

In the case of such headup displays, it is known to form the imageforming unit as a liquid crystal display which produces the imageinformation to be displayed. By means of a light source arranged behindthe liquid crystal display and trans illuminating the liquid crystaldisplay the image information produced by the liquid crystal display isprojected as light beams directly or via an optical projection systemonto a partially reflecting region of a windshield pane in the visualrange of a driver of a motor vehicle and reflected to the driver fromthere. This produces a virtual image, visible to the driver, at aspacing of a few meters approximately in the area of the beginning ofthe radiator hood of the motor vehicle which the driver can view,without a problem, simultaneously with the surround field withoutaccommodating the eyes.

In order for such a virtual image to be effectively detectable in thecase of as far as possible all ambient conditions, in particular highambient brightness, and for alphanumeric characters to be effectivelyreadable, its luminance must as far as possible be greater than 5000cd/m³. On the basis of the light losses at mirrors and/or lenses and atthe windshield pane, this involves a luminance of 20,000-30,000 cd/m³ onthe surface of the liquid crystal display. If the liquid crystal displayis a colored liquid crystal display, a luminance of 500,000 cd/m³ mustbe produced by the light source behind the liquid crystal displaybecause of the low transmission of a colored liquid crystal display of4-5%. In this case, the colored liquid crystal display has a contrast ofless than 150, and this leads to a lit-up background of the liquidcrystal display that has a disturbing effect.

The required high luminance of the backlighting of the liquid crystaldisplay requires a light source of correspondingly large dimensions witha high energy consumption, the large developed heat of which must bedissipated by large heat sinks, fans or other heat dissipators.

Moreover, the design of the headup display is complicated and requires alarge installation space.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to create a headup display ofthe type mentioned at the beginning which has a simple design requiringlittle installation space, permits color displays and exhibits goodreadability with high contrast in all ambient conditions.

This object is achieved according to the invention by virtue of the factthat the image forming unit has an OLED display for forming the imageinformation to be displayed, in front of which there is arranged a lightdirecting element by which the light beams produced by the OLED displaycan be directed approximately parallel to one another.

Since the OLED (organic light emitting diodes) display is aself-luminous display, there is no need either for an additional lightsource or for large heat dissipating devices, and so the design issimple and the required installation space is kept small. Moreover, bycontrast with the use of a liquid crystal display, as a self-luminousdisplay the OLED display requires only a light quantity which isapproximately twenty times less in accordance with the transmittance ofa liquid crystal display.

In particular, a color representation is possible without additionaloutlay.

The neutral background of the OLED display leads to a high contrast, andthus to good readability.

Owing to the light directing element, a colored OLED display may have aluminance which is 10-20 times less than a corresponding backlit coloredliquid crystal display, since the light emitted by the OLED display isfocused by the light directing element into a small solid angle, and isthus raised to a high useful luminance. This can reach 20,000-30,000cd/m³, which leads to a good virtual representation in color.

In order to achieve a good virtual representation, it suffices when thelight beams can be directed at an angle of less than approximately 30°.

In order to reduce the overall space required, the light directingelement can be arranged on the display surface of the OLED displayprojecting the light beams.

The light directing element can either be a flexible transparent film,or else a rigid transparent plate.

In order to reduce a light loss, the light directing element ispreferably applied to the surface of the OLED display without an opticalinterface, since in this case no reflection losses, in particular nototal reflection losses, occur during transition of light from the OLEDdisplay to the light directing element.

To this end, it is possible, in particular, for the light directingelement to be bonded onto the surface of the OLED display.

If the transparent substrate of the OLED display is formed, on the sidethereof projecting the light beams, as light directing element, thiscomponent takes over a double function, and this not only leads to areduction in the components, but also excludes light loss problems byreflection losses of the above-named type.

The light directing element is preferably formed with a light guidingstructure extending over its surface.

It is possible in this case for the light guiding structure to be, in away that is easy to produce, a prismatic, in particular a microprismaticstructure, a lenticular, in particular a microlenticular structure or adirectional reflector structure, in particular a directionalmicroreflector structure.

If the OLED display has a point matrix electrode which is, inparticular, freely programmable, a display of variable image informationof high variability is possible with an appropriately serial drive.

The OLED display can be a fully color-capable display.

In order to achieve a size correction of the image information to berepresented, and to compensate a distortion of the image owing to acurvature of the pane, it can be possible for the light beams to beprojected by the image forming unit via a mirror system onto thepartially reflecting pane, for which purpose the mirror system can haveat least one plane mirror and at least one free form planar mirror.

If a transparent cover is arranged between the mirror system and thepartially reflecting pane, this serves to protect the mirror system.

The transparent cover is preferably arcuately formed in this case inorder to avoid dazzling by the cover pane.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are illustrated in the drawingand will be described in more detail below. In the drawing:

FIG. 1 shows a schematic illustration of a headup display,

FIG. 2 shows a first exemplary embodiment of an image forming unit of aheadup display according to FIG. 1,

FIG. 3 shows a second exemplary embodiment of an image forming unit of aheadup display according to FIG. 1,

FIG. 4 shows a third exemplary embodiment of an image forming unit of aheadup display according to FIG. 1,

FIG. 5 shows an enlarged illustration of the detail “A” from FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The headup display, illustrated in FIG. 1, for a motor vehicle has animage forming unit 1 which has an OLED display 8. The image informationproduced by the OLED display which can, for example, be symbols fortank, temperature and oil level, navigation instructions of a navigationdevice, or else alphanumeric data on the traveling speed or the enginespeed, is projected as light beams 2 via a mirror system with a planemirror 3 and a concave free form mirror 5 which can be rotated about anaxis 4, as well as via an arcuate transparent cover 6 onto a windshieldpane 7, formed to be partially reflecting, of the motor vehicle andreflected by the windshield pane 7 into the field of view of a driver ofthe motor vehicle.

The OLED displays 8′, 8″ and 8′″ illustrated in FIGS. 2 to 5 have a rearsubstrate 9 which can be formed as a plastic film or as a rigid glassplate. Applied to the substrate 9 as rear electrode 10 is a planarelectrode made from metal for example.

The latter bears, in turn, an OLED (Organic Light Emitting Diodes) layer11 which can consist of an organic polymer.

Arranged on the OLED layer 11 is a transparent point matrix electrode 12made from indium-tin-oxide (ITO), for example, which comprises amultiplicity of pixel points which can be driven separately by avoltage. Upon application of a voltage to the rear electrode 10 andindividual pixel points of the point matrix electrode 12, the OLEDmaterial of the OLED layer 11 is excited to emit light in the region ofthe driven pixel points.

The emitted light is radiated to the front side of the OLED display 8′,8″ and 8′″, on which a transparent front substrate 13 is bonded on thepoint matrix electrode 12. The front substrate 13 is formed as a lightdirecting element 14, 14′ and 14″ with a light guiding structureextending over its entire front surface.

In FIG. 2, the light guiding structure is a microlenticular structure 15of mutually adjoining lenses of small size. Instead of themicrolenticular structure in FIG. 2, the light guiding structure in FIG.3 is a microprismatic structure 16 of mutually adjoining prisms of smallsize.

The light guiding structure present in FIGS. 4 and 5 is a directionalmicroreflector structure 17 of reflector elements 18, arranged close toone another, of small size, whose outer surfaces 19 are silvered. Theinclination of the outer surfaces 19 to the plane of the light directingelement 14″ is such that the light beams 2 passing through between thereflector elements 18 and emitted by the OLED layer 11 are radiatedwithin an angle 20 of at most 30° through the silvered outer surfaces 19of the reflector elements 18 in a fashion directed to the front side(FIG. 5).

The light emitted by the OLED layer 11 is likewise radiated within anangle of at most 30° in a fashion directed to the front side by thelenses and prisms in FIGS. 2 and 3.

Because of the microstructure of the light directing elements 14, 14′and 14″, the image projected by the light beams 2 onto the windshieldpane 7 has such a high resolution that the individual pixels cannot beresolved by the eye of the driver, and so a homogeneous image can beseen.

The light directing element can also comprise a layer system which has aplurality of layers and results in a direction of light corresponding tothe light directing elements described above.

1. Headup display, in particular for a motor vehicle, having an imageforming unit for forming an item of image information to be displayedthat is projectable as light beams by the image forming unit directly orvia an optical projection system onto a partially reflecting pane, inparticular onto a windshield pane, wherein the image forming unit (1)has an OLED display (8, 8 ′, 8″, 8′″) for forming the image informationto be displayed, in front of which there is arranged a light directingelement (14, 14 ′, 14″) by which the light beams (2) produced by theOLED display (8, 8 ′, 8″, 8′″) are directable approximately parallel toone another; and the light beams (2) are directable at an angle (20) ofless than approximately 30°.
 2. Headup display according to claim 1,wherein the light directing element (14, 14′, 14 y) is arranged on adisplay surface of the OLED display (8′, 8″, 8′″) projecting the lightbeams (2).
 3. Headup display according to claim 2, wherein the lightdirecting element (14, 14′, 14″) is a transparent film.
 4. Headupdisplay according to claim 2, wherein the light directing element is atransparent plate.
 5. Headup display according to claim 2, wherein thelight directing element (14, 14′, 14″) is applied to the surface of theOLED display (8, 8′, 8-, 8′″) without an optical interface.
 6. Headupdisplay according to claim 5, wherein the light directing element (14,14′, 14″) is bonded onto the surface of the OLED display (8′, 8″, 8′″).7. Headup display according to claim 1, wherein a transparent substrate(13) of the OLED display (8′, 8″, 8′″) is formed, on a side thereofprojecting the light beams (2), as the light directing element (14, 14′,8″).
 8. Headup display according to claim 1, wherein the light directingelement (14, 14′, 14″) is formed with a light guiding structureextending over its surface.
 9. Headup display according to claim 8,wherein the light guiding structure is a prismatic, in particular amicroprismatic structure (16).
 10. Headup display according to claim 8,wherein the light guiding structure is a lenticular, in particular amicrolenticular structure (15).
 11. Headup display according to claim 8,wherein the light guiding structure is a directional reflectorstructure, in particular a directional microreflector structure (17).12. Headup display according to claim 1, wherein the OLED display isfreely programmable.
 13. Headup display according to claim 1, whereinthe OLED display is a fully color-capable display.
 14. Headup displayaccording to claim 1, wherein the light beams (2) are projectable by theimage forming unit (1) via a mirror system onto the partially reflectingpane.
 15. Headup display according to claim 14, wherein the mirrorsystem has at least one plane mirror (3) and at least one free formplanar mirror (5).
 16. Headup display according claim 15, wherein atransparent cover (6) is arranged between the mirror system and thepartially reflecting pane.
 17. Headup display according to claim 16,wherein the transparent cover (6) is arcuate.
 18. Headup display, inparticular for a motor vehicle, having an image forming unit for formingan item of image information to be displayed that is projectable aslight beams by the image forming unit directly or via an opticalprojection system onto a partially reflecting pane, in particular onto awindshield pane, wherein the image forming unit (1) has an OLED display(8, 8′, 8″, 8′″) for forming the image information to be displayed, infront of which there is arranged a light directing element (14, 14′,14″) by which the light beams (2) produced by the OLED display (8, 8′,8″, B′″) are directable approximately Parallel to one another, and theOLED display (8′, 8″, 8′″) has a point matrix electrode (12).